1、编译阶段：
servlet容器编译servlet源文件，生成servlet类。
观察一个JSP页面在第一次访问的时候会由servlet容器会生成.java文件，最终编译成.class字节码文件，如果打开.java文件查看，就是一个servlet。
2、初始化阶段：
加载与JSP对应的servlet类，创建其实例，并调用它的初始化方法。
3、执行阶段：
调用与JSP对应的servlet实例的服务方法。
4、销毁阶段：
调用与JSP对应的servlet实例的销毁方法，然后销毁servlet实例。
如下图所示的是servlet的生命周期和JSP非常的相似：
下面来测试一下JSP实现这些生命周期，在left.jsp页面如下写法：
<%@ page language="java" contentType="text/html; charset=UTF-8" pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<title>life.jsp</title>
</head>
<body> <%!
private int initVar=0;
private int serviceVar=0;
private int destroyVar=0;
%> <%!
public void jspInit(){
initVar++;
System.out.println("jspInit(): JSP被初始化了"+initVar+"次");
}
public void jspDestroy(){
destroyVar++;
System.out.println("jspDestroy(): JSP被销毁了"+destroyVar+"次");
}
%> <%
serviceVar++;
System.out.println("_jspService(): JSP共响应了"+serviceVar+"次请求"); String content1="初始化次数 : "+initVar;
String content2="响应客户请求次数 : "+serviceVar;
String content3="销毁次数 : "+destroyVar;
%>
<p><%=content1 %></p>
<p><%=content2 %></p>
<p><%=content3 %></p> </body>
</html>
效果如下：
然后打开工作空间的生成的java文件：“\workspace_web_test\.metadata\.plugins\org.eclipse.wst.server.core\tmp0\work\Catalina\localhost\webtest1\org\apache\jsp\life_jsp.java”
会发现如下结构：
/*
* Generated by the Jasper component of Apache Tomcat
* Version: Apache Tomcat/7.0.68
* Generated at: 2016-12-14 13:18:33 UTC
* Note: The last modified time of this file was set to
* the last modified time of the source file after
* generation to assist with modification tracking.
*/
package org.apache.jsp; import javax.servlet.*;
import javax.servlet.http.*;
import javax.servlet.jsp.*; public final class life_jsp extends org.apache.jasper.runtime.HttpJspBase
implements org.apache.jasper.runtime.JspSourceDependent { private int initVar=0;
private int serviceVar=0;
private int destroyVar=0; public void jspInit(){
initVar++;
System.out.println("jspInit(): JSP被初始化了"+initVar+"次");
}
public void jspDestroy(){
destroyVar++;
System.out.println("jspDestroy(): JSP被销毁了"+destroyVar+"次");
} private static final javax.servlet.jsp.JspFactory _jspxFactory =
javax.servlet.jsp.JspFactory.getDefaultFactory(); private static java.util.Map<java.lang.String,java.lang.Long> _jspx_dependants; private volatile javax.el.ExpressionFactory _el_expressionfactory;
private volatile org.apache.tomcat.InstanceManager _jsp_instancemanager; public java.util.Map<java.lang.String,java.lang.Long> getDependants() {
return _jspx_dependants;
} public javax.el.ExpressionFactory _jsp_getExpressionFactory() {
if (_el_expressionfactory == null) {
synchronized (this) {
if (_el_expressionfactory == null) {
_el_expressionfactory = _jspxFactory.getJspApplicationContext(getServletConfig().getServletContext()).getExpressionFactory();
}
}
}
return _el_expressionfactory;
} public org.apache.tomcat.InstanceManager _jsp_getInstanceManager() {
if (_jsp_instancemanager == null) {
synchronized (this) {
if (_jsp_instancemanager == null) {
_jsp_instancemanager = org.apache.jasper.runtime.InstanceManagerFactory.getInstanceManager(getServletConfig());
}
}
}
return _jsp_instancemanager;
} public void _jspInit() {
} public void _jspDestroy() {
} public void _jspService(final javax.servlet.http.HttpServletRequest request, final javax.servlet.http.HttpServletResponse response)
throws java.io.IOException, javax.servlet.ServletException { final javax.servlet.jsp.PageContext pageContext;
javax.servlet.http.HttpSession session = null;
final javax.servlet.ServletContext application;
final javax.servlet.ServletConfig config;
javax.servlet.jsp.JspWriter out = null;
final java.lang.Object page = this;
javax.servlet.jsp.JspWriter _jspx_out = null;
javax.servlet.jsp.PageContext _jspx_page_context = null; try {
response.setContentType("text/html; charset=UTF-8");
pageContext = _jspxFactory.getPageContext(this, request, response,
null, true, 8192, true);
_jspx_page_context = pageContext;
application = pageContext.getServletContext();
config = pageContext.getServletConfig();
session = pageContext.getSession();
out = pageContext.getOut();
_jspx_out = out; out.write("\r\n");
out.write("<!DOCTYPE html PUBLIC \"-//W3C//DTD HTML 4.01 Transitional//EN\" \"http://www.w3.org/TR/html4/loose.dtd\">\r\n");
out.write("<html>\r\n");
out.write("<head>\r\n");
out.write("<title>life.jsp</title>\r\n");
out.write("</head>\r\n");
out.write("<body>\r\n");
out.write("\r\n");
out.write("\r\n");
out.write(" \r\n");
out.write("\r\n");
out.write("\r\n"); serviceVar++;
System.out.println("_jspService(): JSP共响应了"+serviceVar+"次请求"); String content1="初始化次数 : "+initVar;
String content2="响应客户请求次数 : "+serviceVar;
String content3="销毁次数 : "+destroyVar; out.write("\r\n");
out.write("<p>");
out.print(content1 );
out.write("</p>\r\n");
out.write("<p>");
out.print(content2 );
out.write("</p>\r\n");
out.write("<p>");
out.print(content3 );
out.write("</p>\r\n");
out.write("\r\n");
out.write("</body>\r\n");
out.write("</html>");
} catch (java.lang.Throwable t) {
if (!(t instanceof javax.servlet.jsp.SkipPageException)){
out = _jspx_out;
if (out != null && out.getBufferSize() != 0)
try {
if (response.isCommitted()) {
out.flush();
} else {
out.clearBuffer();
}
} catch (java.io.IOException e) {}
if (_jspx_page_context != null) _jspx_page_context.handlePageException(t);
else throw new ServletException(t);
}
} finally {
_jspxFactory.releasePageContext(_jspx_page_context);
}
}
}
参考：